Mechanical device for an engine ignition timer



y 23, 196': L. A. BEVACQUA 3,320,770

MECHANICAL DEVICE FOR AN ENGINE IGNITION TIMER Filed July 12, 1965 2 Sheets-Sheet l y 1957 L, A. BEVACQUA 3,320,770

MECHANICAL DEVICE FOR AN ENGINE IGNITION TIMER Filed July 12, 1965 2 Sheets-Sheet 2 REES.

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FLYWHEEL DEG United States Patent 3,320,770 MECHANICAL DEVICE FOR AN ENGINE IGNITION TIMER Louis A. Bevacqua, Des Plaines, lll., assignor to Motorola, Inc., Franklin Park, Ill., a corporation of Illinois Filed July 12, 1965, Ser. N0. 470,994 7 Claims. (Cl. 64-25) This invention pertains generally to a centrifugal advance mechanism, and more particularly to a centrifugal advance mechanism for the ignition timer of an automoble engine, which both advances and retards the timer at different engine speeds.

Reduction of smog in large cities has become an increasingly important problem. To meet this problem it is highly desirable that automobile engines be designed to operate so that the hydrocarbons which are emitted in the exhaust from the engines are substantially reduced. One way to reduce this emission of hydrocarbons in the exhaust is by retarding the engine ignition timing during the time that the car is idling, for instance, when stopped in heavy traflic or at a trafiic light.

Present ignition timers have the spark advance set at the manufacturers recommended position for starting and then advance the spark with increased engine r.p.m. Therefore, the engine ignition is the same during idling as at starting, or slightly advanced with respect to the starting position. To retard the timing further at starting would present the problem of hard starting, loss of power and overheating at high rpm.

It is an object of this invention to provide an improved centrifugal advance mechanism for an automobile ignition timer.

It is another object of this invention to provide a centrifugal mechanism for an engine ignition timer that can be produced at a reasonable cost and which acts to retard the ignition timing with respect to the position for starting while idling, and then to advance the engine timing with increased engine r.p.rn.

One feature of this invention is the provision of a centrifugal mechanism having a first rotatable member with weights pivotally mounted thereon and a second rotatable member coaxially and rotatably mounted with respect to said first member, so that outward movement of the weights as the first member rotates is transmitted through a linkage to cause the second member to rotate relative to said first member first in one direction, and then in a direction opposite to said one direction.

Another feature of this invention is the provision of a centrifugal mechanism having pinion gears connected to the weights and an idler gear mounted on the first member, rotating therewith and in engagement with the pinion gears, so that outward movement of the weights is transmitted through the gear train thereby insuring that the weights move in equal amount to provide high sensitivity of the device at a low rotation rate of the first member.

Still another feature of this invention is the provision of a centrifugal advance mechanism having first and second pairs of weights, with one weight of each pair pivotally mounted to a rotatable drive plate and the second weight of each pair piovtally mounted to an interruptor advance plate. A first pivot post couples the first pair of weights and a second post slidably and pivotally couples the second pair of weights. With initial movement of the weights in an outwardly direction, the distance between the pivotal mountings of the first pair of weights increases, and upon continued outward movement of the weights the distance between the mountings decreases causing the desired relative movement of the rotatable drive plate with respect to the interruptor ad- 3,320,770 Patented May 23, 1967 vance plate thereby initially retarding and then advancing the engine ignition timing.

A further feature of this invention is the provision of a centrifugal advance mechanism having a radial slot in the drive plate and a calculated curved slot in the interruptor advance plate superimposed on the radial slot. A first pivot post coupled to the first pair of weights passes through the radial and curved slots and is slidable therein. With outward movement of the weights the pivot post slides in the radial slot thereby displacing the curved slot to cause the desired relative movement of the drive plate with respect to the interruptor advance plate to retard and advance the engine ignition timing.

In the drawings:

FIG. 1 is a side elevation of the centrifugal advance mechanism of this invention;

FIG. 2 is a plan view of the mechanism of FIG. 1 with the movement of the weights shown in dotted lines;

FIG. 3 is a plan view of a modification of the device of FIG. 2;

FIG. 4 is a plan view of a second embodiment of the mechanism of FIG. 1 with the movement of the weights shown in dotted lines;

FIG. 5 is a plan view of a third embodiment of the mechanism of FIG. 1 with the movement of the weights shown in dotted lines;

FIG. 6 is a plan view of the radial and calculated slots shown in FIG. 5; and

FIG. 7 is a graph illustrating the operation of th mechanism of the invention.

In accordance with this invention, a centrifugal mechanism is provided for an ignition timer of an internal combustion engine and includes a rotatable drive plate with weights pivotally mounted thereon and an interruptor advance plate coaxially and rotatably mounted with respect to the drive plate. The interrupter advance plate is connected through a shaft to a cam rotatably mounted on an interruptor plate that supports the pulsing mechanism. With the engine at rest the cam and pulsing mechanism are in a position to one another to provide optimum starting for the engine. As the drive plate rotates at a speed proportional to the engine r.p.m., linkage between the weights and the advance plate rotates the latter at the same speed, and centrifugal force moves the weights in an outwardly direction. This movement is translated through the linkage causing the interruptor advance plate to rotate relative to the drive plate, first in a direction to move the cam to retard the ignition timing and then in a direction to move the cam to advance the ignition timing.

The linkage for translating the motion of the weights to move the interruptor advance plate relative to the drive plate may take on various forms. For instance, a simple link may be pivotally connected to the weight and to the interrupter advance plate, with the pivot point selected so that initial outward motion of the weights will move the advance plate to retard the timing, and continued outward motion of the weights will move the advance plate in a direction to advance the timing. In another embodiment, one of a pair of weights is pivotally mounted to the drive plate and the other Weight is pivotally mounted to the advance plate and both weights are pivotally joined to each other. Initial movement of the weights in an outwardly direction increases the distance between the pivots joining the weights to the plates to retard the engine timing and continued outward movement of the plates decreases the distance between the same pivots to advance the ignition timing. In a further embodiment, an arm is coaxially and rotatably mounted between the drive plate and the advance plate. One weight of a pair is pivotally mounted to the drive plate with the other weight pivotally mounted to the arm, and a pivot post pivotally joins the weights to each other. There is a radial slot in the drive plate and a calculated :urved slot in. the advance plate superimposed on the radial slot. The pivot post joining the weights passes through the radial and curved slots and is slidable therein. With outward movement of the plate, the pivot posts slide :in the radial and curved slots thereby displacing the curved slots to first retard and then to advance the ignition timing.

The device of the invention is described for use as a centrifugal mechanism for an automobile ignition timer. It should be understood that this device may find utility in other applications where a centrifugal mechanism is desirable.

In FIG. 1 an interruptor shaft 14, with. an interruptor advance plate 16 fixedly mounted thereto is coaxially and rotatably mounted with respect to a drive shaft 19. A drive plate 12 is fixedly mounted to the shaft 10. A cam 17 is integral with the shaft 14 and turns with the shaft to operate the ignition timing points 15, mounted on the interruptor plate 13, in the known manner. Two weights 18 and 20 are pivotally connected to the drive plate 12 by pivot projections 21 and 22. Pinion gears 24 and 25 are connected to the weights and mounted to the pivot projections 21 and 22 in a similar fashion. Anidler gear 26 is coaxially and rotatably mounted to drive shaft 10, disposed on plate 12 and rotatably engaged with the pinion gears. A link 28 (FIG. 2) is pivotally mounted to the weight 18 by post 30 and to plate 16 by post 31. Post 31 is free to slide in groove 33 in plate 12 as the advance plate 16 rotates. relative to plate 12. A spring 32' is mounted to the weight 18 by post 30 and to the plate 12 by projection 22. A second spring 36 is connected to plate 16 by spring post 34 and to plate 12 by spring post 38.

Referring to FIG. 2, with the engine at rest, the timing is set at the manufacturers recommended position for starting. As the shaft turns at a rate equal to the engine r.p.m. while idling, for exampleat 300 r.p.m., the weights 18 and are forced outward by centrifugal force to the position indicated by the dashed line at 40. The initial outward movement of weight 18 is transmitted through link 28'to move the interruptor advance plate 16 in a clockwise direction until the pivot projection 21 and the posts 30 and 31 lie in a straight line, at which time the are described by post 30 rotating about projection 21 is tangent to the arc described by post 30 rotating about post 31, resulting in no relative motion between the two plates. This clockwise movement of the interruptor advance plate 16 is transmitted through interruptor shaft 14 to rotate cam 17 to retard the spark and corresponds to the position when-the engine is idling. With continued outward motion of the weight 18 due to increased engine r.p.m., the post 30 moves off the line shown between post 21 and post 31 thereby moving the advance plate 16 through link 28 in a counter clockwise direction relative to the drive plate 12 to advance the spark as indicated by the dotted and dashed line 42. This position corresponds to the manufacturers recommended advance for optimum operation at speeds other than idle.

The spring 32 resists the outward motion of the weight 18 and, indirectly through the gear train, weight 20. The spring 32 cooperates with the spring 36 and resists the advance of the interruptor advance plate 16 to provide a method for adjusting the timing to correspond to the manufacturers recommended curve as the engine r.p.m. increases.

The weight 20 serves two functions. First, its pivot projection 22 is diametrically disposed on plate 12 to pivot projection 21 so that as the weights swing out, the weight 20 will compensate for the weight 18 thereby balancing the drive plate 12. Secondly, by not having weight 20 spring connected to plate 12 as is weight 18,

it will swing out from the center of plate 12 faster than will weight 18. This motion is transmitted through pinion gear 25 and idler gear. 26 to turn pinion gear 24 thereby moving weight 18 to the same outward position as weight 20. This action provides for greater sensitivity of the device at idling speeds and is desirable because the center of gravity of the weights 18 and 20 is near the center of drive plate 12 Where centrifugal force has the least effect.

A variation of this invention is shown in FIG. 3. The pinion gears 24 and 25 and the idler gear 26 are removed, and a spring 44 is connected to t-he drive plate 12 by spring post 21 and to the weight 20 by post 46. The operation of the device is the same as described above, with the exception that spring 44 resists the outward movement of weight 20 to the same degree as spring 32 resists the same movement of weight 18, thereby permitting weight 20 to balance the drive plate 12.

A second embodiment is shown in FIG. 4. In this embodiment two pairs of weights 50, 51 and 52, 53 are used. Weights 51 and 52 are pivotally mounted to the plate 12 by pivot projections 55 and 56 respectively. Weights 50 and 53 are pivotally mounted to the interruptor advance plate 16 by pivot projections 58 and 59 respectively. A pivot post 60 pivotally couples the weights 50 and 51, and a pivot post 62 connected to weight 52 pivotally couples weights 52 and 53. Weight 53 has a slot 64 into which pivot post 62 can slide. Spring 66 is mounted to the weights 50 and 51 by post 60 and to the drive plate 12 by projection 56. Spring 67 is mounted to the weights 52 and 53 by the :post 62 and to the plate 12 by projection 55. A third spring 36 is connected to the interruptor advance plate 16 by spring post 34 and to drive plate 12 by spring post 38.

With the engine at rest the timing is set at the manufacturers recommended position for starting. Starting the engine initiates the movement of the weights 50, 51 and 52, 53 pivotally about posts 60 and 62 and outwardly due to centrifugal force. This initial outward movement increases the distance between the pivot projections 55 and 58 to rotate the interruptor advance plate 16 counter clockwise relative to the drive plate 12 which retards the spark as indicated by the dashed line 40. When the pivot post 60 moves to a position where it lies on a line drawn between the pivot projections 55 and 58, the counter clockwise motion stops. Further outward movement of the weights 50 and 51 due to the increased engine rpm. moves the post 60 of the aforementioned linethereby decreasing the distance between the pivot projections 55 and 58 to move the plate 16 clockwise relative to the drive plate 12, which advancesthe spark as indicated by the dotted and dashed lines 42. As the weights 52 and 53 move in an outward direction to balance the plate 12, the pivot post 52 initially. slides into the 'slot 64 in weight 53 and then out of the slot 64 upon continued outward motion of the weights, such that this outward movement of the weights '52, 53 does not aifect the distance between projections 56 and 59. The springs 66, 67 and 36 function as described in the first embodiment.

A third embodiment of the invention is shown in FIG. 5. An arm 70 is rotatably mounted with respect to the drive shaft 10 and disposed between the plate 12 and the plate 16. Two pairs of weights 72, 73 and 74, 75 are used. Weights 73 and 74 are pivotally mounted to the plate 12 by pivot projections 77 and 78 respectively. Weights 72 and 75 are pivotallymounted to the arm 70 by pivot projections 76 and 79 respectively. Spring 86 is mounted to the weights 72 and 73 by post 84 and to the drive plate 12 by projection 78. Spring 87 is mounted to the weights 74 and 75 by post 85 and to the drive plate 12 by projection 77. A third spring 36 is connected to the interruptor advance plate 16 by spring post 34 and to drive plate 12 by spring. post 38. The drive plate 12 has a radial slot in it which coincides with the are that Weight 73 describes when rotated about projection 77. The interruptor advance plate 16 has a calculated curve slot 82 in it that is superimposed on the radial slot 80. A pivot post 84 pivotally couples the weights 72 and 73 and extends through the radial slot 80 and the curve slot 82 and is slidable therein. A second pivot post '85 pivotally couples the weights 72 and 75.

With the engine at rest, the timing is set at the manufacturers recommended position for starting. Starting the engine initiates the movement of the weights 72, 73 and 74, 75 pivotally about posts 84 and 85 and outwardly due to centrifugal force. This outward movement of the weights 72 and 73 causes pivot post 84 to slide in radial slot 80 and curve slot 82 thereby displacing the curved slot to rotate the interruptor advance plate 16 counter clockwise relative to the drive plate 12 thereby retarding the spark. Further outward movement of the weights 72 and 73 causes the curved slot 80 to 'be further displaced thereby rotating the plate 16 clockwise relative to the drive shaft to advance the spark as indicated by the dotted lines 42.

The arm 70 compensates for the sliding motion of the pivot post 84 in the radial slot 80 to maintain the pivot projections 76, 77 and 78, 79 in the same relative position with respect to one another. This permits the outward motion of the weights 74 and 75 to properly balance the drive plate 12, as indicated by the positions of the arm 70 in FIG. 5 for varying engine rpm. The springs 86, 87 and 36 function as described in the first embodiment.

Although this invention and its embodiments have been described with the weights and drive plate 12 located above interruptor advance plate 16, thereby providing easy access, it should be understood that the Weights could be placed below the interruptor plate 13 if desired, or in any other suitable arrangement of drive plate 12, interruptor advance plate 16 and the Weights. It should also be understood from the above de'sscription that this invention will function equally as well with the drive shaft 10 rotating in a clockwise or counter clockwise direction while developing the centrifugal force.

The principle operation of the invention may be better understood by referring to the graph of FIG. 7. The changes of flywheel degrees is plotted against the engine speed in 'r.p;m., with the dotted line *90 indicating the standard advance recommended by the manufacturer, and the solid line 92 indicating the advance and retarding action of this invention. Using a standard ignition advance mechanism, the engine of the vehicle is started with the ignition timing as indicated at 94 and remains at the recommended position for starting during the idle range, or until the engine r.p.m. is about 700 a indicated at 96. At this point the timing is advanced by increased engine r.p.m. along line 97.

With the centrifugal advance mechanism of this invention, however, the vehicle is started at the manufacturers recommended position for starting '94. The timing remains in this position during cranking or until about 300 rpm. When the cranking motor is de-energized, the engine timing is retarded 10 (-point 99) by the centrifugal force of the weights moving outwardly as described. The curve between points 99 and 100 is relatively flat representing the period where the engine rpm. is increased from the idling range but is still not great enough to overcome the tension of the springs to advance the timing. However, as the engine r.p.m. increases from the idling range at point 100 the ignition timing is rapidly advanced. This is shown by line 92 which continues to rise rapidly until the two curves merge (point 102). From point 102, the timing is advanced in accordance with the manufacturers recommendation.

What has been described, therefore, is an improved centrifugal advance mechanism that permits starting an automobile at manufacturers recommended timing, then retarding the ignition timing below that of the manufacturers recommended position while idling, and then advancing the timing with increased engine r.p.m. in accordance with the manufacturers recommendation.

I claim:

1. A centrifugal mechanism including in combination, a first shaft with a first plate fixedly mounted thereto, a second shaft with a second plate fixedly mounted thereto, said second shaft being coaxial with and rotatably mounted with respect to said first shaft, and coupling means for rotating said second plate relative to said first plate including centrifugal weights at least one of which is pivotally mounted to said first plate, first spring means connecting said weights to said first plate, a spring post mounted to said second plate, second spring means connecting said post to said first plate, and linking means coupled to said weights and to said second plate and responsive to initial movement of said weights in an outwardly direction for moving said second plate in one direction relative to said first plate, said first spring means resisting said outward movement of said weights, said linking means being responsive to continued outward movement of said Weights for moving said second plate relative to said first plate in the direction opposite to said one direction, and said second spring means resisting said relative movement of said second plate in the direction opposite to said one direction.

2. A centrifugal mechanism including in combination, a first shaft with a first plate fixedly mounted thereto, a second shaft with a second plate fixedly mounted thereto, said second shaft being coaxial with and rotatably mounted with respect to first shaft, actuating means for rotating said second plate relative to said first plate including centrifugal weights at least one of which is pivotally mounted to said first plate, first spring means con necting said weights to said first plate, a spring post mounted to said second plate, second spring means connecting said post to said first plate, and linking means including pivots for pivotally connecting said linking means to said first and second plates, said linking means being responsive to initial movement of said weights in an outwardly direction for moving said second plate in one direction relative to said first plate, said first spring means resisting said outward movement of said weights, said pivots of said linking means becoming aligned with said pivotal mounting of at least one of said Weights to said first plate thereby stopping said movement of said second plate relative to said first plate, said linking means being responsive to continued outward movement of said Weights for moving said pivots of said linking means out of alignment with said pivotal mounting thereby moving said second plate relative to said first plate in the direction opposite to said one direction, and said second spring means resisting said relative movement of said second plate in the direction opposite to said one direction.

3. A centrifugal advance mechanism for an engine ignition timer, including in combination, a drive shaft With a drive plate fixedly mounted thereto, a second shaft with an advance plate fixedly mounted thereto, said second shaft being coaxial with and rotatably mounted with respect to said drive shaft, first and second pairs of centrifugal weights and first and second pairs of pivot projections with said first pair of projections mounted to said drive plate and said second pair of projections mounted to said advance plate, with one weight of each pair pivotally mounted to said drive plate by said first pair of pivot projections and the second weight of each pair pivotally mounted to said advance plate by said second pair of pivot projections, coupling means including a first pivot post pivotally coupling said first pair of weights and a second pivot post slidably and pivotally coupling said second pair of weights, first and second springs respectively connecting said first and second pivot posts with said drive plate, a spring post mounted to said advance plate, and a third spring connecting said spring post to said drive plate, with initial movement of said weights n an outwardly direction increasing the distance between aid first and second pivot projections of said first pair of veights to move said advance plate in one direction relaive to said drive plate to retard the ignition timing, and :ontinued outward movement of said weights decreasing he distance between said first and second pivot projecions to move said advance plate relative to said drive late in the direction opposite to said one direction to ldvance the ignition timing, said outward movement of aid weights causing said second pair of weights topivot llld slide'about said second pivot post thereby balancing aid drive plate without affecting the distance between .aid first and second pivot projections of said second pair )f weights, with said first and second springs resisting iaid outward movement of said weights, and said third ipring resisting said relative movement of said drive plate n the direction opposite to said one direction.

4. A centrifugal advance mechanism for an engine gnition timer including in combination, a drive shaft with i drive plate fixedly mounted thereto, a second shaft with in advance plate fixedly mounted thereto, said second aha-ft being coaxial with and rotatably mounted with re-. ipect to said drive shaft, two centrifugal weights pivotally nounted to said drive plate and diametrically disposed hereon, a link pivotally mountedto one of said weights 1nd to said advance plate, a first spring connecting said am of said weights to said drive plate, a spring post nounted to said advance plate, and a second spring coniecting said spring post to said drive plate, an-idler gear rotatably and coaxially mounted with respect to said drive shaft and disposed on said first plate, and a pair of pinion gears connected to said centrifugal weights and engaged with said idler gear, with initial movement of said weights in an outwardly direction being transmitted :hrough said pinion gears to said idler gear thereby proliding a high sensitivity of the device at a low rotation rate of said drive plate, said movement causing said link move said advance plate in one direction relative to said drive plate, and continued outward movement of said weights causing said link to move said advance plate relative to said'drive plate in the direction opposite to said one direction, with said first spring resisting said outward movement of sad weights, and said second spring resisting said relative movement of said advance plate in the direction opposite to said one direction.

5. 'A centrifugal advance mechanism for an engine ignition timer including in combination, a drive shaft with a drive plate fixedly mounted thereto, a second shaft with an advance plate fixedly mounted thereto, said second shaft being coaxial with and rotatably mounted with respect to said drive shaft, two centrifugal weights pivotally mounted to said drive plate and diametrically disposed thereon, a link pivotally mounted to one of said weights and to said advance plate, first and second springs each resiliently connecting one of said weights to said drive plate, a spring post mounted to said advance plate, and a third spring connecting said spring post to said drive plate, with initial movement of said weights in an outwardly direction causing said link to move said advance plate in one direction relative to said drive plate, and continued outward movement of said weights causing said link to move said advance plate relative to said drive plate in the direction opposite to said one direction, with said first and second springs resisting said outward movement of said weights, and said third spring resisting said relative movement of said advance plate in the direction opposite to said one direction.

6. A centrifugal advance mechanism for an ignition timer including in combination, a drive shaft with a drive plate fixedly mounted thereto, a second shaft with an advance plate fixedly mounted thereto being coaxially with and rotatably mounted with respect to said drive shaft, an arm rotatably m unted with respect to said drive shaft,

said arm being disposed between said drive plate and said advance plate, first and second pairs of centrifugal weights and first and second pairs of pivot projections, with said first pair of pivot projections mounted to said drive plate and said second pair of projections mounted to said arm, with one weight of each pair pivotally mounted to said drive plate by said first pair of pivot projections, and the second weight of each pair pivotally mounted to said arm by said second pair of pivot projections, a radial slot in said drive plate and a calculated curved slot in said advance plate superimposed on said radial slot, coupling means including .a first pivot post pivotally coupling said first pair of weights, said post passing through saidradial and curved slots and being slidable therein, and a second pivot post coupling said second pair of weights, first and second springs respectively connecting said first and second pivot posts with said drive plate, a spring post mounted to said advance plate, and a third spring connecting said protrusion to said drive plate, with initial movement of said weight in an outwardly direction sliding said first pivot post in said radial and curved slots thereby displacing said curved slot in said advance plate to move the same in one direction relative to said drive plate, and continued outward movement further displacing said curved slot to move said advance plate relative to said first plate in the direction opposite to said one direction, said outward movement of said weights causing said second pair of weights to pivot about said second pivot post thereby balancing said drive plate, with said arm compensating for said sliding motion of said first pivot post in said radial slot to maintain said pairs of pivot projections in the same relative position with respect to one another.

7. A centrifugal mechanism including in combination, a first shaft with a first plate fixedly mounted thereto, a second shaft with a second plate fixedly mounted thereto, said second shaft being coaxial with and rotatably mounted with respect to said first shaft, and coupling means for rotating said second plate relative to said first plate including centrifugal weights at least one of which is pivotally mounted to said first plate, first spring means connecting said weights to said first plate, second spring means connecting said second plate to said first plate, and linking means coupled to said weights and to said second plate and responsive to initial movement of said weights in an outwardly direction for moving said second plate in one direction relative to said first plate, said first spring means resisting said outward movement of said'weights, said linking means being responsive to continued outward movement of said weights for moving said second plate relative to said first plate in the direction opposite to said one direction, and said second spring means resisting said relative movement of said second plate in the direction opposite to said one direction.

References Cited by the Examiner UNITED STATES PATENTS 2,393,344 1/1946 Scott 6425 2,533,755 12/1950 Bange 6425 2,549,749 4/1951 Spengler 6425 2,549,750 4/ 1951 Spengler 6425 2,677,946 5/ 1954 Purdy 6425 References (Iited by the Applicant UNITED STATES PATENTS 1,962,931 6/1934 Mallory. 2,167,366 7/1939 Mallory. 3,027,884 4/1962 Bale et al.

FRED C. MATTERN, JR., Primary Examiner.

HALL C. COE, Examiner. 

1. A CENTRIFUGAL MECHANISM INCLUDING IN COMBINATION, A FIRST SHAFT WITH A FIRST PLATE FIXEDLY MOUNTED THERETO, A SECOND SHAFT WITH A SECOND PLATE FIXEDLY MOUNTED THERETO, SAID SECOND SHAFT BEING COAXIAL WITH AND ROTATABLY MOUNTED WITH RESPECT TO SAID FIRST SHAFT, AND COUPLING MEANS FOR ROTATING SAID SECOND PLATE RELATIVE TO SAID FIRST PLATE INCLUDING CENTRIFUGAL WEIGHTS AT LEAST ONE OF WHICH IS PIVOTALLY MOUNTED TO SAID FIRST PLATE, FIRST SPRING MEANS CONNECTING SAID WEIGHTS TO SAID FIRST PLATE, A SPRING POST MOUNTED TO SAID SECOND PLATE, SECOND SPRING MEANS CONNECTING SAID POST TO SAID FIRST PLATE, AND LINKING MEANS COUPLED TO SAID WEIGHTS AND TO SAID SECOND PLATE AND RESPONSIVE TO INITIAL MOVEMENT OF SAID WEIGHTS IN AN OUTWARDLY DIRECTION FOR MOVING SAID SECOND PLATE IN ONE DIRECTION RELATIVE TO SAID FIRST PLATE, SAID FIRST SPRING MEANS RESISTING SAID OUTWARD MOVEMENT OF SAID WEIGHTS, SAID LINKING MEANS RESPONSIVE TO CONTINUED OUTWARD MOVEMENT OF SAID WEIGHTS FOR MOVING SAID SECOND PLATE RELATIVE TO SAID FIRST PLATE IN THE DIRECTION OPPOSITE TO SAID ONE DIRECTION, AND SAID SECOND SPRING MEANS RESISTING SAID RELATIVE MOVEMENT OF SAID SECOND PLATE IN THE DIRECTION OPPOSITE TO SAID ONE DIRECTION. 